In the construction of enclosed buildings, it is generally most efficient to construct the columns, floors, roof, and internal supporting walls initially and thereafter to enclose the structure by constructing the exterior walls. Curtain walls have been developed which are prefabricated and erected in modules of a manageable size and weight. The wall modules are of a height generally equal to the building's storey height. Each module is supported by connectors upon the outer area of the building floor. Modules are stacked upon each other in parallel rows and adjacent modules are often mechanically connected together. The gap between adjacent modules is sealed with caulking to provide a weather proof exterior wall.
Although, modules may be constructed as load bearing exterior walls, commonly in higher buildings, each building floor supports a row of modules of a height equal to the building's storey height. In general, most buildings are composed of planar vertical exterior walls and the walls are constructed in rectangular modules. Although, the description herein relates to exterior walls of such rectangular modules, it will be understood that wall modules of this type may be constructed in any form (with a curved or an angular surface, for example) and that such modules also may be utilized in constructing interior walls (in atrium structures, for example).
Conventional curtain wall modules comprise a frame having a horizontal top chord, a horizontal bottom chord and a plurality of vertical transverse studs spaced at intervals along the length of the chords thereby defining a plurality of panels. The top and bottom ends of each stud are nested within and connected to the top and bottom chords respectively by spot-welding or with mechanical connectors. The chords and studs are generally light channel sections made of roll-formed galvanized sheet steel. Additional frame members may be used to frame openings for windows and doors.
Exterior cladding of various types is mounted to the exterior face and exposed edges of the frame. The cladding may comprise rigid insulation, gypsum board, plywood, foam insulation, and fabric reinforcing to form a solid backing for a variety of weatherproof finishes applied to the backing such as split bricks, stucco or epoxy resins.
Windows and doors may be installed within the openings in the frame during prefabrication in an indoor factory or shop. The completely fabricated wall module is relatively light, and therefore, even though the module has a low section modulus longitudinally, the chords are generally of sufficient strength to avoid lateral buckling or excessive deflection during handling and installation. The design live load from wind induces stresses in the module many times greater than those stresses induced by the module's dead load. Since the governing load is wind load the sheet metal channel studs are designed to have adequate capacity to resist transverse bending loads in their installed state being supported at both ends by the chords. In conventional modules to prevent overstressing of the chords under the load imposed by the studs, the chords are connected to the floors of the building at multiple points spaced along the length of the module to ensure that the wind loads are transmitted from the studs to the chords then to the building. When a module is overstressed or deflects excessively the cladding may be torn from the connectors and the frame, and the relatively brittle cladding may crack and delaminate.
Stresses also may be introduced in the modules by differential settlement or deflection of the supporting floors of the building. When multiple connections are used the light weight modules are forced to conform to the shape of the floor and buckling or failure of the module's cladding may occur. The building floors may settle or deflect under live loads, due to concrete creeping, or due to foundation settlement.
To minimize the risk of damage in shipping the completed wall modules are shipped to the building site in an inclined position approximately 70.degree.-80.degree. to horizontal upon A-frame truck trailers. The wall modules are lifted by a crane at the building site and installed on supporting brackets attached to the outer edges of the building's floors.
Due to the relatively low resistance of the chords of conventional wall modules to bending stress, such wall modules must be connected to the building floors at several points along their lengths. In this way, lateral buckling of the chords is prevented and vertical deflection of the module between connections is reduced to acceptable levels. Large numbers of support connections must be fabricated and installed for each module consuming materials and time. Since the available time for installation at a building site is usually limited by construction schedules, and the cost of labour is relatively expensive; a connection design which requires multiple support points reduces the cost efficiency of such prefabricated curtain walls, as well as rendering the module prone to failure when the supporting structure settles or deflects differentially.
In order to strengthen conventional wall modules, structural members of strength greater than the chords and studs have been introduced to reinforce the modules. Commonly, a rolled angle iron or channel section, or a hollow structural section is attached to the periphery of the module connected parallel to both chords at least and may also be connected parallel to the outer studs to fully encircle the frame. Such a conventional design increases the resistance to lateral buckling, vertical deflection and bending. In addition, such a module requires fewer connections since the structural members span between connections supporting the relatively light frame. A frame which includes structural members along the full length of the top and bottom chords, and which may include transverse outer structural members along the outer studs is significantly more complicated to fabricate and is heavier than a module lacking such reinforcing. The conventional reinforced module is therefore significantly more expensive to fabricate and the building structure must be of sufficient structural strength to support the additional weight of the modules.
Conventional connectors used in association with reinforced modules include a short angle iron with attached reinforcing bar or welded studs embedded in the outer edge of the concrete floors of the building. A short member of angle or channel is placed extending transversely to the module. The module is suspended from a crane during installation. The extending member is welded to the embedded angle and is welded to the inner face of the structural member of the suspended module. After welding is completed, the module is released from the crane. The module is suspended from the cantilevering extending member which is itself supported by the embedded angle in the floor of the building. The field welding of the connector to the module allows for a large degree of adjustment and alignment of individual panels during installation and the reinforced module need only be connected to the building in this way at two points along the length of the structural member to support the weight of the module. The disadvantages of such field welded connections are that a crane is fully occupied during alignment and welding and subsequent correction to the positioning of the module is very difficult. Welding the extending member to the outer face of the building's structural member is preferred since the outer face is generally the only face that is accessible and downhand welding may be performed avoiding difficult overhead or hidden welding positions. However, connecting to the outer face of the structural member induces torsional stresses in the structural member and in the module. These torsional and transverse bending stresses are accommodated by increasing the torsional strength of the structural member and increasing the strength of the studs and connections to the building.
It is, therefore, desirable to provide a wall module that is resistant to bending, buckling and vertical deflection during handling and in its installed condition, that is relatively light weight, and is easily fabricated.
It is also desirable to provide a wall module which requires as few connectors as possible requiring intrusion upon the building structure design in order to reduce design, material and labour costs, especially during site construction.
It is also desirable to provide a wall module having connections which do not induce additional stresses into the modules and connections in order to minimize the necessary strength and weight of the modules.
It is also desirable to provide a wall module having connectors which enable adjacent modules to be aligned and positioned relative to each other in a rapid manner in order to reduce site construction costs and installation time.